In a voice control system controlling a target device by recognizing a speech uttered by a user, as shown in FIG. 9, as the user utters the speech as a command through a microphone Z1, a speech recognition engine (SR engine) Z2 recognizes the uttered speech as a recognized command to output the recognized command to a device-manipulating signal generating unit Z3. The SR engine Z2 simultaneously instructs a speech synthesis engine (SS engine) Z4 to synthesize a piece of speech synthesis data that notifies that the uttered speech of the user is recognized and to output it to a speaker Z5. The user can thereby confirm that the uttered speech is successfully recognized.
The signal generating unit Z3 then outputs, based on the recognized command outputted by the SR engine Z2, a control signal to a target device Z6. An operating state of the target device Z6 is thereby changed based on the control signal. When changing of the operating state is completed, the target device Z6 outputs a signal notifying the completion of changing the operating state to the SS engine Z4. The SS engine Z4 synthesizes a piece of speech synthesis data, which notifies the completion of changing the operating state, and outputs it to the speaker Z5. The user can thereby confirm that the operating state of the target device Z6 is changed.
However, in the above case, the then operating state of the target device at a time when the uttered speech is recognized is not considered. Therefore, when the user utters a command that is unable to be executed in the operating state of the time, problems are imposed as follows.
For instance, it is supposed that the user utters a radio station of an FM mode while an AM mode of the radio is received. Here, the speech synthesis engine Z4 talks back, as an echo message, a name of the radio station of the FM mode as soon as the uttered radio station is successfully recognized. However, since the radio station of the FM mode cannot be selected at the AM mode, an advisory message that, after the current AM mode is shifted into the FM mode, the radio station of the FM mode should be selected is announced. Here, the user feels unpleasant about voice manipulation since the advisory message indicating failure of the voice manipulation is announced posterior to the echo massage indicating that the uttered speech is successfully recognized. It is furthermore supposed that, while an audio is turned on (in an ON state), the speech recognition engine Z2 mis-recognizes “TURN OFF AUDIO” uttered by the user as a command of “TURN ON AUDIO.” Here, an advisory message of “AUDIO IS ALREADY TURNED ON” is then announced. Here, since the operating state of the device of the time is not considered, the advisory message ends up in being inappropriate or showing being mis-recognized.